The present invention relates to a magnetic tunnel junction magneto-resistive head using a magneto-resistive (MR) sensor based on magnetic tunnel junction effect as a read sensor and its manufacturing method.
In accordance with increasing high density of a magnetic storage apparatus in recent years, a spin valve type magneto-resistive sensor, which uses giant magneto-resistive (GMR) effect, is put to practical use for a read sensor. Further, in order to realize future high density, it is popular to develop a magneto-resistive sensor based on tunneling magneto-resistive (TMR) effect.
The magnetic tunnel junction effect is the phenomenon that in case of the forming of a junction where an insulating junction layer lies between two ferromagnetic layers, its junction resistance depends on the angle between the magnetization directions of two ferromagnetic layers. The phenomenon exhibits that the junction resistance becomes the minimum when the magnetization directions of two ferromagnetic layers are in parallel, the junction resistance becomes the maximum when they arc in anti-parallel each other, and the junction resistance becomes medium between the minimum and the maximum when they are in medium between parallel and anti-parallel directions. Hereafter, such the stack of the layers is defined as Magnetic Tunneling Junction Stack that exhibits this kind of phenomenon and comprises two ferromagnetic layers and an insulating junction layer (insulating tunnel barrier layer) laid between them.
The Magnetic Tunneling Junction Stack is formed on a lower electrode on a substrate which is a stacked structure with plural layers and contacted with an upper electrode. An electric current is input to either of the lower electrode or the upper electrode and is returned to the other electrode through the Magnetic Tunneling Junction Stack. Magnetically recorded information is read out by detecting a voltage signal between the two electrodes.
First ferromagnetic layer composing the Magnetic Tunneling Junction Stack, which is called as a pinned ferromagnetic layer, has an antiferromagnetic layer on the opposite side to the junction layer, and its magnetic moment is prevented from spinning under the magnetic field applied within the range of desired amount by an exchange coupling bias field of the antiferromagnetic layer. And the second ferromagnetic layer, which is called as a free ferromagnetic layer, does not have an antiferromagnetic layer on the opposite side of the junction layer, and its magnetic moment is free to spin under the magnetic field applied within the range of desired amount. The magnetic moment of the pinned ferromagnetic layer is positioned toward the direction to cross an air-bearing surface approximately at right angles. Besides, from the point of view of a good read signal, the free ferromagnetic layer is preferred to be a single magnetic domain and the magnetic moment is preferred to be in parallel to the air-bearing surface when no magnetic field is given.
As an example of prior art, a structural drawing of a view from an air-bearing surface of the structure disclosed by JP-B-10-162327 is shown in FIG. 6.
The magnetic tunnel junction magneto-resistive read head in FIG. 6 has a Magnetic Tunneling Junction Stack unit 300 which is formed as a stack between a lower electrode 102 formed on a substrate of a gap layer G1 and an upper electrode 104 formed under a gap layer G2. The Magnetic Tunneling Junction Stack unit 300 comprises a pin layer 310, an insulating tunnel barrier layer 320, a free ferromagnetic layer 330 and a protective layer 360.
The pin layer 310 formed so as to contact the lower electrode 102 has a seed layer 312 on the lower electrode 102, a layer of an antiferromagnetic material on the seed layer 312 and a ‘pinned’ ferromagnetic layer, which is formed on the antiferromagnetic layer 316 and exchange biased. This ‘pinned’ ferromagnetic layer is named as a pinned ferromagnetic layer 319 since its magnetic moment is prevented from spinning under the magnetic field applied within the range of desired amount. The magnetic moment of this pinned ferromagnetic layer 319 is positioned toward the direction to cross the air-bearing surface approximately at right angles.
According to the prior art, a hard magnetic material 350 is arranged on both sides of the Magnetic Tunneling Junction Stack in view from the air-bearing surface and the magnetic moment of the free ferromagnetic layer is controlled to be the desired direction by the magneto-static coupling with the free ferromagnetic layer 330 in order to make the free ferromagnetic layer 330 to be a single domain structure and to set its magnetized direction to be in parallel to the air-bearing surface. Because of using a conductive material as a hard magnetic material such as CoPtCr, there exists a bypassed current which does not go through the tunnel junction if the Magnetic Tunneling Junction Stack is contacted directly with the hard magnetic material, so that such the current is useless to a resistance variation and makes the sensitivity of a sensor decrease. Therefore, an insulating layer 370 of Al2O3 or SiO2 is applied between these layers to prevent from a electric contact between the hard magnetic material layer and the Magnetic Tunneling Junction Stack.
As another example of the prior art, there is JP-B-10-255231. According to this example, as well as the described prior art, a hard magnetic material layer or an antiferromagnetically coupling layer is arranged on both sides of a free ferromagnetic layer. However, the size of a pinned ferromagnetic layer is formed to be smaller than the free ferromagnetic layer.
In case of the magnetic tunnel junction magneto-resistive head of Abutted junction type as disclosed by JP-B-10-162327, the hard magnetic material 350 is arranged on each of both sides of the Magnetic Tunneling Junction Stack through the inserted insulating layer 370. If the insulating layer becomes thicker, the distance between the hard magnetic material layer 350 and the free ferromagnetic layer 330 becomes longer, so that the magneto-static coupling becomes less, the domain controlling force to the free ferromagnetic layer 330 becomes weaker, and then Barkhousen noise appears in the read signal waveform. On the other hand, if the distance between the hard magnetic material layer 350 and the free ferromagnetic layer 330 becomes closer, the domain controlling force to the free ferromagnetic layer 330 becomes stronger. However, the insulation breakdown voltage between the hard magnetic material layer and the Magnetic Tunneling Junction Stack becomes lower, so that there increases the possibility not to achieve the expected performance because of the insulation breakdown during the manufacturing process or the practical use.
Therefore, according to the construction shown by JP-B-10-162327, there is a problem that it is difficult to realize the magnetic moment control of the free ferromagnetic layer in conjunction with keeping enough insulation between the hard magnetic material layer and the Magnetic Tunneling Junction Stack.
In addition in case that the pinned ferromagnetic layer is formed smaller than the free ferromagnetic layer and the hard magnetic material is arranged on both sides of the free ferromagnetic layer as shown in JP-B-10-255231, it is possible to overcome the problem of the bypassed current through the hard magnetic material layer, however, it is practically difficult to form the pinned ferromagnetic layer as smaller than the free ferromagnetic layer since so highly difficult process technique is required that it is necessary to etch selectively the pinned ferromagnetic layer without etching of the free ferromagnetic layer from a body formed as a stack of the pinned ferromagnetic layer and the free ferromagnetic layer.